This invention is generally directed to toner compositions and developer compositions, as well as the use of these compositions in electrostatographic imaging systems including color imaging processes. More specifically, the present invention is directed to toner compositions containing therein, as charge enhancing additives, certain ion binding polymers. These additives which are effective in incorporating (binding) salts into dielectric resins can, in conjunction with the bound salt, cause the toner particles to assume a positive or negative triboelectric charge, and further are non-toxic, thermally stable, and desirably homogeneously dispersed. Positive charging toner compositions with the ion binding polymer/salt complexes of the present invention are particularly useful in electrostatographic imaging systems having incorporated therein a Viton.RTM.-coated fuser roll, since the additives involved do not react with the Viton.RTM., causing undesirable decomposition thereof, which adversely affects image quality. Negatively charged toner compositions comprised of the ion binding polymer/salt charge complexes are particularly useful in colored imaging processes.
Electrostatographic processes, and more specifically the xerographic process, are well known as documented in several prior art references. This process involves development of an electrostatic latent image by applying toner particles to the image to be developed using, for example, cascade development, magnetic brush development, and touchdown development. The toner particles applied can be charged negatively or positively, depending upon the charge deposited on the photoreceptor surface. Thus, for example, when it is desired to develop a negatively charged imaging surface, the toner particles are positively charged usually by incorporating therein certain charge enhancing additives. In contrast, when developing a positively charged imaging surface, the toner particles are negatively charged usually by incorporating therein charge enhancing additives which will cause the toner particles to assume negative charges thereon.
Numerous charge enhancing additives are disclosed in the prior art including those which impart a positive charge to the toner composition. For example, there is disclosed in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium compounds as charge control agents for electrostatic toner compositions. According to the disclosure of this patent, certain quaternary ammonium compounds when incorporated into toner materials were found to provide a toner composition which exhibited a relatively high uniform and stable toner charge when mixed with a suitable carrier particle. A similar teaching is present in U.S. Pat. No. 4,079,014 with the exception that there is added to the toner composition as a charge control agent a diazo compound.
Additionally, there is disclosed in U.S. Pat. No. 4,298,672 toner compositions with alkylpyidinium compounds as positive charge enhancing additives. According to the disclosure of this patent, there is incorporated into the toner composition in an amount of, for example, up to about 10 percent by weight the charge enhancing additive cetyl pyridinium chloride. Moreover, there is disclosed in U.S. Pat. No. 4,338,390 toner compositions containing as charge enhancing additives various organic sulfate or organic sulfonate compositions. In accordance with the disclosure of this patent there is incorporated into the toner composition, for example, 10 percent by weight of various organic sulfate or sulfonate compounds, including stearyl dimethylphenethyl ammonium para-toluenesulfonate. These additives impart a positive triboelectric charge to the toner resin particles, and further are compatible with Viton.RTM. fuser systems.
Charge enhancing additives which permit toner particles to assume negative charges are also known. There is described, for example, in the prior art negative charge enhancing additives comprised of an ortho-halo phenylcarboxylic acid, and the use of developer compositions with such additives for causing the development of colored images in xerographic imaging systems. Additionally, in U.S. Pat. No. 4,454,214 there is disclosed toner compositions, including magnetic toner compositions and colored toner compositions comprised of a thermally stable tetrafluoroborate charge enhancing additive. Positive charging toner compositions with these additives, especially the additive cetyl pyridinium tetrafluoroborate, are useful in electrostatographic imaging systems having incorporated therein a Viton.RTM. coated fuser roll, since the tetrafluoroborates involved do not react with the Viton.RTM., causing undesirable decomposition thereof.
While many charge enhancing additives are known, especially those additives which impart a positive charge to the toner resin particles, there continues to be a need for new charge control additives, particularly those additives which are non-toxic, thermally stable, and can be homogeneously dispersed in the toner resin particles. Furthermore, there continues to be a need for new charge enhancing additives which will not interact with Viton.RTM. type fuser rolls, and wherein the resulting toner and developer compositions are humidity insensitive, since it is known that moisture contained in the atmosphere or moisture from other sources can adversely affect the electrical properties of the toner compositions involved. Moreover, while the charge enhancing additives described in the prior art are suitable for their intended purposes, that is for imparting, for example, a positive charge to the toner resin particles, some of these additives are toxic, interact with certain fuser rolls incorporated into the electrostatographic imaging system, are not thermally stable, and cannot desirably be homogeneously dispersed in the toner resin particles. Specifically, for example, it is known that certain prior art charge enhancing additives adversely affect Viton.RTM. fuser rolls, causing a deterioration in the quality of the images developed in electrostatographic copying systems with these rolls. Thus, for example, Viton.RTM. fuser rolls discolor and turn black as well as develop multiple surface cracks when developer compositions with several of the prior art charge enhancing additives contact the Viton.RTM. fuser roll.
An example of one type of Viton.RTM. fuser roll used in electrostatographic copying machines is comprised of a soft roll fabricated from lead oxide and DuPont Viton.RTM. E-430 resin, a vinylidene fluoride, and hexafluoropropylene copolymer. Approximately 15 parts of lead oxide and 100 parts of the Viton.RTM. E-430 are blended together and cured on a roll at elevated temperatures. Apparently the function of the lead oxide is to generate unsaturation by dihydrofluorination and to provide crosslinking sites for binding of release fluid. Excellent image quality has been obtained with such Viton.RTM. fuser rolls, however, in some instances there is a toner fuser compatibility problem when charge control agents are contained in the toner mixture. For example, it is believed that certain quaternary ammonium charge control additives, and alkylpyridinium compounds or degradation products thereof react with the Viton.RTM. fuser roll. Thus, an alkylpyridinium chloride such as cetyl pyridinium chloride when included in the toner mixture appears to attack the fuser roll resulting in an increased unsaturation in the Viton.RTM. which subsequently crosslinks and looses its compliance. As a result, the Viton.RTM. fuser turns black and develops multiple surface cracks resulting in image quality deterioration.
Additionally, it is known that many quaternary ammonium salts are thermally unstable, this instability being dependent upon the alkyl substituents and the gegen ion present therein. Most quaternary ammonium salts are susceptible to the Hoffman degradation reaction wherein undesirable noxious amine byproducts are generated. Furthermore, although quaternary ammonium salt charge enhancing additives are dispersable in resinous toner polymers, they are to a large degree insoluble in such polymers, and therefore the bulk of the salt exists in the toner as small crystallites. Accordingly, the charging characteristics of the final toner composition are substantially dependent on the manner in which the toner is prepared, that is, toners prepared by extrusion, roll milling, or Banbury mixing may have different charging characteristics. Additionally, the inhomogeneity of mixtures of toner resins and quaternary ammonium salts can, in certain situations, contribute to poor developer composition aging. This inhomogeneity tends to cause the dispersed quaternary ammonium salts to be transported through the imaging apparatus undesirably contaminating all subsystems including the photoreceptor, the fuser, and the corona wires.
Accordingly, there thus continues to be a need for improved charge enhancing additives for incorporation into toner compositions and developer compositions. Additionally, there continues to be a need for charge enhancing additives which provide a positive or negative triboelectric charge to the toner resin particles depending on, for example, the nature of the host polymer in which the bound salt is dispersed. Also, there continues to be a need for toner and developer compositions which contain charge enhancing additives that are non-toxic, do not adversely affect fuser rolls, and in particular Viton.RTM. fuser rolls selected for use in electrostatographic imaging systems, are thermally stable; and wherein the charge enhancing additives are immobile. Additionally, there is a need for charge enhancing additive which can be prepared by a simple direct, economical process, thereby decreasing the cost of the toner compositions generated. Furthermore, there continues to be a need for toner compositions which will rapidly charge new uncharged toner particles which are added to a positively charged toner composition or negatively charged toner compositions. Moreover, there continues to be a need for toner compositions comprised of charge enhancing additives which will allow development of electrostatic latent images, either positively charged or negatively charged, with a wide spectrum of toner resins.